1. Field of the Invention
The present invention relates generally to noise analyzers for video produced by imaging systems and, in particular, to analyzers suitable for quantifying the noise present in video produced by an X-ray imaging system.
2. Description of the Related Art
X-ray imaging systems of the type suitable for examination of patients employ relatively low X-ray dose levels to irradiate the patient in order to limit the patient's exposure. As a consequence of employing such low dose levels, the X-ray images that are produced, on film or otherwise, may exhibit noticeable X-ray quantum noise.
X-ray imaging systems of a type utilizing an X-ray image intensifier and camera chain to detect the X-ray image and to produce a video image are being employed in a growing number of examinations. In addition to the availability of X-ray images as a real time display on a monitor, for example in fluoroscopy applications, electronic image processing and/or archiving in a mass storage device may be implemented in radiologic applications. The images produced by such systems may exhibit electrical noise introduced by the image intensifier and camera chain in addition to the X-ray quantum noise.
While it is possible to judge qualitatively from observation whether an image has excessive noise, no equipment is known for providing a quantitative measure of the noise present in a video image. Further, apparent noisiness may vary spatially within an X-ray image, and inhomogeneity in a test phantom may be misinterpreted or mismeasured as noise.
In commonly-owned U.S. Pat. No. 5,144,430, a device and method are disclosed for generating an operator positionable marker signal in a video image to serve as an oscilloscope trigger.